1. Field of the Invention
The present invention pertains to methods and apparatus for making shade guides. More particularly, the present invention relates to techniques for constructing samples of ceramic materials, such as porcelain, and particularly provides a technique for constructing such samples on a metal or ceramic base, for example. The porcelain samples so produced are readily usable as shade samples whereby the shade of a porcelain formation may be anticipated so that appropriate porcelain powders may be slected to achieve the desired shade.
2. Description of the Prior Art
Dental prostheses, including crowns and "false teeth" mounted on a bridge or plate, are generally made, at least in part, utilizing porcelain as a close approximation of the finish of natural teeth. For both terapeutic and cosmetic purposes, the prosthesis is generally shaped to approximate the shape of the tooth, or portion thereof, which the prosthesis is replacing. It is also important for cosmetic purposes that the coloring of the prosthesis match the remaining portion of the natural tooth to which the prosthesis is being added, or, in the case of a complete cap or complete prosthesis, that the color match the remaining teeth and/or prostheses in the mouth.
Typically, porcelain prostheses are made by dental technicians utilizing one or more powders mixed with water or other liquid to form the porcelain. The dentist must convey to the technician appropriate information to enable the technician to reproduce the desired prosthetic coloring. The technician may even have access to the patient to carry out the color matching. The selecting of coloring is done by selection of the powder or powders obtained from the manufacturer of same, the different porcelain powders providing different coloring when mixed with liquid, formed and fired in a kiln in the usual fashion of constructing porcelain finishes. Thus, the technician must know in advance which powder or powders to use to obtain a porcelain prosthesis finished with the desired coloring.
Various manufacturers currently provide samples of the porcelain finishes in the form of tabs made from the different powders supplied by the respective manufacturers. The intention is that the technician, or dentist, may compare the various tabs, referred to as shade tabs, to the desired coloring and then, based on the comparison, select the powder or powders to use to construct the prosthesis. However, it may be expected that each manufacturer's powders are unique, and further that powders of the same kind from a given manufacturer, although intended to be consistent, may vary from batch to batch. The result is that a dental technician may be required to acquire a shade tab for each powder from each batch of porcelain powders obtained from a given manufacturer. Additionally, where the technician must mix two or mor powders to achieve a porcelain finished with a particular coloring, the technician would most certainly have to obtain a shade tab utilizing such a mixture to anticipate its coloring.
A currently available form for molding a porcelain sample is shown generally at 10 in FIG. 1. The form 10 is essentially a slab of elastic material with one or more (two are shown) shaped recesses 12 into which a mixture of ceramic powder and liquid may be positioned to form a stylized tooth shape of the type generally used as shade tab samples. The flexibility of the form allows the hardened porcelain to be readily removed for firing.
Another forming device currently available is shown generally at 14 in FIG. 2, and includes a metal body 16 with two arms 18 and 20 extending from one end thereof to define a recess 22 between the arms. Moistened ceramic powder is pressed into the recess 22 which again takes the general stylized tooth shape. A planar member 24, also of metal, is connected to the body 16 by an axle 26 so that the member 24 may be selectively moved under the recess 22 as illustrated, or turned aside as shown in phantom to open the recess from the bottom. The member 24 is used as a convenience in forming the porcelain mixture within the recess 22, but may be replaced by tissue paper or the like held under the recess as the procelain is molded in place. The top surfaces of the arms 18 and 20 are sloped to facilitate forming a tapered stylized tooth shape, if desired, by permitting a flat surface to be moved over or pressed against the ceramic material in the recess 22.
Each of the molding tools illustrated in FIGS. 1 and 2 may be used to produce a porcelain-only shade tab of the type generally provided by porcelain powder manufacturers. However, the shade of a prosthesis is somewhat complex, referring to the hue, or color, of the finished product, its chroma, or intensity of hue, and the amount of grayness as opposed to whiteness that appears in the finish porcelain, which quantity is referred to as the value of the shade. Determination and anticipation of these shade qualities in the case of a porcelain sample for use in constructing a dental prosthesis are complicated by the fact that such prostheses are not entirely constructed from porcelain, with the exception of some cases including porcelain jacket crowns, and "false teeth" constructed to be mounted on a plate or the like. In general, a cap, or crown, is built up by first forming a metal or ceramic base which is shaped to fit over the remnant of the tooth root that remains after preparation of the tooth for capping. The base is covered with an intermediate layer of opaque ceramic material to mask the metal or ceramic substructure, and the finish porcelain, which is exposed and visible, is built up on the intermediate layer. The entire cap can then be fired and glazed in a kiln, and mounted on the root remnant by cementing the base to the remnant.
While only the finish porcelain surface is directly visible with the prosthesis properly mounted in the mouth of the patient, nevertheless, the opaque layer contributes to the shading of the finished prosthesis including one or more of the features of hue, chroma and value. For example, a finish porcelain layer, which may be somewhat translucent, may look darker, that is, exhibit more grayness, on an opaque layer over a ceramic base than a like finish layer on the same base without an opaque underlayer. In the more common case of a metal base, the finish layer directly on the base would appear darker than a finish layer over an opaque intermediate ceramic layer. Shade tabs currently acquired by dental technicians or constructed by them are generally made solely of the porcelain which will be used only in the finish layer of the prosthesis. Consequently, the effect of an opaque intermediate layer does not contribute to the shading of the ceramic shade samples currently being used.
It is desirable and would be highly advantageous for dental technicians to have available shade tabs constructed generally as caps or crowns are constructed, that is, with a finish porcelain layer overlying an intermediate opaque ceramic layer which in turn is mounted on a metal or ceramic backing. Further, it would be desirable and advantageous for the dental technician to have the capability of readily and rapidly making such structured shade tabs utilizing the various porcelain powders currently available from manufacturers as needed. Such capabilities for manufacturing shade tabs that more accurately reflect the shading of finished prosthesis would further aid the technician in customizing shading of prosthesis by mixing two or more such manufacturers' powders to achieve the desired coloring, since a source of error inherently a part of current shade tab technology, that is, the lack of consideration for the contribution of the opaque ceramic layer of the prosthesis, could be avoided.